The basic objective of the total project is to determine what, if any, effects 1-alpha acetylmethadol (LAAM) and/or its primary metabolites noracetylmethadol and nor.noracetylmethadol have on the cardiovascular system. The first part of the project has consisted of experiments in which the direct chronotropic actions of LAAM were investigated. The isolated right atrium of the guinea pig was used for thi purpose. The results of these studies indicate that LAAM, as well as methadone, can alter rhythmic activity in this preparation. Morphine did not appear to have an effect on such activity. The effects of these three compounds on the chronotropic responses to catecholamines were studied also.